1. Field of the Invention
The present invention relates to periodic dielectric structures and, in particular to optical notch filters made of nanochannel glass material having a two-dimensional array of rods in a matrix.
2. Background of the Related Art
Currently, notch filters are generally made by vacuum deposition of multilayer dielectric films on a transparent substrate. These filters have very limited useful acceptance angles since the spectral properties are angle-dependent; in fact, they are generally useful only for collimated light sources, especially when the notches in the transmission are narrow. In addition, the multilayer dielectric film filters are very sensitive to environmental factors such as heat, humidity and mechanical contact, and their optical properties degrade easily. They are particularly difficult to clean since some of the materials used for the thin-film layers are soft and easily damaged by scratching. Finally, the multilayer dielectric film filters are easily damaged by high-power sources, such as many lasers.
A dielectric filter comprising a two-dimensional lattice structure is described in U.S. Pat. No. 5,389,943, the disclosure of which is incorporated herein by reference. The structure is formed by boring holes in a high dielectric material or by stacking and aligning sheets of high dielectric material having holes bored therein. Therefore, the frequency range that can be filtered by such a structure is necessarily limited by the size of the holes that can be drilled.
A two-dimensional photonic band structure consisting of a triangular lattice of circular air rods (∈1=1.0) in a matrix of microchannel Pbxe2x80x94O glass (∈2=2.6) is described in Inoue et al xe2x80x9cFabrication of Two Dimensional Photonic Band Structure with Near-Infrared Band Gapxe2x80x9d Jpn. J. Appl. Phys. Vol. 33 (1994) pp L 1463-L 1465.
It is an object of the invention to provide spectral filters having band gaps from the infrared to the ultraviolet.
It is another object of the invention to provide band-gap spectral filters comprising periodic dielectric elements wherein the size, shape, separation and index of refraction of the periodic dielectric elements can be selected to control the width, depth and sharpness of the band gap.
It is another object of the invention to provide band-gap spectral filters that are rugged and resistant to damage from environmental conditions.
It is another object of the invention to provide band-gap spectral filters that are insensitive to the direction of propagation of light.
It is another object of the invention to provide band-gap spectral filters that are highly sensitive to the direction of propagation of light.
The above objects are accomplished by a band-gap spectral filter comprising a nanochannel glass structure having a two-dimensional array of parallel dielectric rods having a first refractive index, arranged in a matrix material having a second refractive index, wherein the difference between the first refractive index and the second refractive index is equal to or less than about 0.7.